Booster device

ABSTRACT

A booster device for increasing a voltage at a voltage supply point of a power supply circuit for supplying a driving voltage to an electronic control circuit is provided. The power supply circuit includes a series-connected circuit having a diode, a resistor, and a capacitor which is connected to a DC power supply. One end of the capacitor is connected to a ground and a connection point of the resistor and the capacitor serves as the voltage supply point. The booster device includes a clamp circuit, an oscillation circuit, and a booster circuit that increase a voltage output from the DC power supply. When the voltage at the voltage supply point falls below a predetermined threshold voltage, the booster device supplies the increased voltage at the voltage supply point.

BACKGROUND

The present invention relates to a booster device for suppressing areduction in an output voltage of a DC power supply when the outputvoltage is decreased.

For example, an electronic component installed into a vehicle is drivenby an electric power being fed from a battery (DC power supply). In suchbattery, a battery voltage is decreased because a large electric currentis output from the battery during the starter cranking. Further, whensuch a condition is combined together that an ambient temperature islow, in some cases the battery voltage is decreased to about 3 to 4 Vfrom 12 to 14 V as the voltage in a normal condition. For this reason,the battery cannot feed the voltage that various electronic componentsinstalled into the vehicle need. Concretely, a lowest operating voltageof the electronic components such as a control circuit, semiconductorswitches, and the like installed into the vehicle is normally about 6 V,so that in some cases the battery cannot normally operate theseelectronic components when the battery voltage is decreased to about 3to 4 V.

Then, an explanation will be made in detail with reference to FIG. 6hereunder. FIG. 6 is a circuit diagram showing a configuration of a loaddriving circuit in the related art. As shown in FIG. 6, a MOSFET (T101)is provided between a battery 106 (output voltage VB) and a load Rz, anda gate of the MOSFET (T101) is connected to a control IC 101. Normally,an NMOS is employed as the MOSFET(T101). Also, the control IC 101includes a charge pump 102 for driving the NMOS, an overcurrentprotection circuit 103 for protecting the MOSFET (T101) and wirings froman overcurrent, a control logic circuit 104, and a driver 105. Then,ON/OFF of the MOSFET (T101) is switched by the ON/OFF operation of aswitch SW1.

Also, a positive-side output terminal (drain of the MOSFET) of thebattery 106 is connected to a ground via a diode DA1, a resistor RA1,and a capacitor CA1. Then, a connection point between the resistor RA1and the capacitor CA1 is connected to the control IC 101. That is, astabilized voltage VBB is generated by a circuit that consists of thediode DA1, the resistor RA1, and the capacitor CA1, and this voltage VBBis used as a power supply voltage of the control IC 101. The voltage VBBis given by VBB=VB−Vf1, where Vf1 is a forward voltage drop of diodeDA1. In this case, a voltage drop in the resistor RA1 is neglectedbecause a resistance value of the resistor RA1 is about 3.9 Ω.

Here, in the condition that the output voltage VB of the battery 106 isdecreased due to the starter cranking, or the like, a decrease of thevoltage VBB can be prevented by the diode DA1 and the capacitor CA1 whenthis reduction time is a short time. However, when a decrease of theoutput voltage VB of the battery 106 extends over a long time thatexceeds 1 second, the electric charges accumulated in the capacitor CA1are consumed by the control IC 101, and thus the voltage VBB isdecreased.

A constant voltage circuit, a constant current circuit, an amplifiercircuit, etc. are contained in the control IC 101, and a large number ofelectronic components such as operational amplifiers, comparators, etc.are used. Therefore, a head room and a foot room of these componentsmust be ensured, and a lowest operating voltage becomes about 6V in thenormal control IC.

In contrast, the output voltage VB of the battery 106 is decreased toabout 3 to 4 V at a time of starter cranking, as described above.Therefore, in order to operate normally the circuits in the control IC101 by this voltage, the head room and the foot room of the operationalamplifiers and the comparators must be made smaller, and thus theoperational amplifiers and the comparators must be designed to have aspecial configuration. This situation yields an increase in cost of theIC. Also, when the voltage VBB is decreased, a boosting capability ofthe charge pump 102 is lowered. Therefore, the number of step-up stagesof the charge pump 102 must be increased. This situation also results inan increase in cost.

[Patent Literature 1] JP-A-2006-5581

As described above, in the load driving circuit in the related art, whenthe output voltage of the DC power supply (e.g., the battery) isdecreased for some reason (e.g., the starter cranking) and then fallsbelow the lowest driving voltage that is applicable to drive theelectronic component (e.g., the element provided in the control IC), insome cases such output voltage cannot cause respective electroniccomponents to operate normally. As a result, the demand that a reductionin the output voltage of the DC power supply should be suppressed by allmeans is escalating.

SUMMARY

The present invention has been made to solve such problem in the relatedart, and it is an object of the present invention to provide a boosterdevice capable of suppressing a reduction in an output voltage of a DCpower supply when the output voltage is decreased.

In order to achieve the above object, according to the presentinvention, there is provided a booster device for increasing a voltageat a voltage supply point of a power supply circuit for supplying adriving voltage to an electronic control circuit, the power supplycircuit including a series-connected circuit having a diode, a resistor,and a capacitor, wherein the series-connected circuit is connected to aDC power supply, and wherein one end of the capacitor is connected to aground and a connection point of the resistor and the capacitor servesas the voltage supply point,

the booster device comprising:

a booster circuit that increases a voltage output from the DC powersupply and supplies the voltage to the voltage supply point,

wherein, when the voltage at the voltage supply point falls below apredetermined threshold voltage, the booster circuit increases thevoltage at the voltage supply point.

According to the present invention, there is also provided a boosterdevice for increasing a voltage at a voltage supply point of a powersupply circuit for supplying a driving voltage to an electronic controlcircuit (IC), the power supply circuit including a firstseries-connected circuit having a diode, a resistor, and a capacitorwhich is connected to a DC power supply, wherein one end of thecapacitor is connected to a ground and a connection point of theresistor and the capacitor serves as the voltage supply point,

the booster device comprising:

a clamp circuit that outputs a drive disabling signal when the voltageat the voltage supply point is equal to or greater than a predeterminedthreshold voltage, and outputs a drive enabling signal, which isgenerated by inverting the drive disabling signal, when the voltage atthe voltage supply point is smaller than the threshold voltage;

an oscillation circuit that outputs a pulse signal when the driveenabling signal is output from the clamp circuit; and

a booster circuit that increases the voltage at the voltage supply pointby supplying electric charges, which are accumulated by a voltage outputfrom the DC power supply, to the voltage supply point when the pulsesignal is output from the oscillation circuit.

Preferably, wherein the clamp circuit includes: a secondseries-connected circuit having a Zener diode (ZD1), a first resistor(R21), and a second resistor (R22), and provided between the voltagesupply point and the ground; and a first switching element (Q10) havinga control electrode which is connected to a connection point of thefirst resistor and the second resistor, and the first switching elementis switched to ON/OFF in response to a voltage generated in the secondresistor. The clamp circuit outputs the drive disabling signal when thefirst switching element is in an ON state, and outputs the driveenabling signal when the first switching element is in an OFF state.

Preferably, the oscillation circuit includes a first capacitor (C1)which is charged when the drive enabling signal is supplied to the firstcapacitor; a second switching element (Q1) which is turned ON based on acharging voltage of the first capacitor (C1); and a third switchingelement (Q2) which is turned OFF when the second switching element (Q1)is turned ON. The first capacitor (C1) starts discharging thereof whenthe third switching element (Q2) is turned OFF, and starts chargingthereof again when the second switching element (Q1) is turned OFF dueto a voltage drop of the first capacitor (C1) and then the thirdswitching element (Q2) is turned ON, so that repetition ofcharging/discharging operations outputs the pulse signal.

Preferably, the oscillation circuit includes the first capacitor (C1)provided between an output terminal of the clamp circuit and the ground,a parallel circuit, a third series-connected circuit, a fourthseries-connected circuit and a fifth series-connected circuit. Theparallel circuit includes a first series connection having a thirdresistor (R1), a fourth resistor (R2), and a second switching element(Q1) and a second series connection having a fifth resistor (R5), asixth resistor (R6), and a third switching element (Q2). The firstseries connection is connected in parallel with the second seriesconnection, one end of the parallel circuit is connected to the voltagesupply point (P2) and other end of the parallel circuit is connected toa seventh resistor (R3). A control electrode of the second switchingelement (Q1) is connected to an output terminal of the clamp circuit,and one end of the second switching element (Q1) is connected to thecontrol electrode of the third switching element (Q2) via a twelfthresistor (R4). The third series-connected circuit includes a fourthswitching element (Q3) whose control electrode is connected to aconnection point of the third resistor (R1) and the fourth resistor(R2), an eighth resistor (R9), and a ninth resistor (R10), one end ofthe third series-connected circuit is connected to the voltage supplypoint (P2) and other end of the third series-connected circuit isconnected to the ground. The fourth series-connected circuit includes afifth switching element (Q4) whose control electrode is connected to aconnection point of the fifth resistor (R5) and the sixth resistor (R6),a tenth resistor (R7), and a first diode (D1), and one end of the fourthseries-connected circuit is connected to the voltage supply point (P2)and other end of the fourth series-connected circuit is connected to theoutput terminal of the clamp circuit. The fifth series-connected circuitincludes a second diode (D2), an eleventh resistor (R8), and a sixthswitching element (Q5), and one end of the fifth series-connectedcircuit is connected to the output terminal of the clamp circuit andother end is connected to the ground. A control electrode of the sixthswitching element (Q5) is connected to a connection point of the eighthresistor (R9) and the ninth resistor (R10). A connection point of theeleventh resistor (R8) and the sixth switching element (Q5) serves as anoutput point of the pulse signal.

Preferably, the booster circuit includes a second capacitor (C2) and athird capacitor (C3), one ends of which are connected to the DC powersupply and other ends of which repeat alternately grounded/non-groundedstates in accordance with a change of ON/OFF of the pulse signal. Thebooster circuit supplies electric charges, which are charged when theother end of the second capacitor (C2) is grounded, to the thirdcapacitor (C3) when the other end of the second capacitor (C2) ischanged into the non-grounded state, and charges the electric charges,which are supplied from the second capacitor (C2) into the thirdcapacitor (C3) when the other end of the third capacitor (C3) isgrounded. The booster circuit supplies the electric charges to thevoltage supply point (P2) to increase the voltage at the voltage supplypoint (P2) when the other end of the third capacitor (C3) is changedinto the non-grounded state.

In the booster device according to the present invention, even in thesituation that the output voltage of the DC power supply is decreasedand thus the voltage (VBB) at a power feed point is decreased to thelevel at which the electronic control circuit cannot operate normally,the booster device is operated to increase the voltage VBB when thevoltage VBB is below the threshold voltage Vth. Therefore, theelectronic control circuit can operate normally with the output voltage.Also, there is no need that the special IC that is operable normallyeven when the voltage VBB is decreased. Therefore, such a situation canbe avoided that an increase in cost is brought about.

BRIEF DESCRIPTION OF THE DRAWINGS

The above objects and advantages of the present invention will becomemore apparent by describing in detail preferred exemplary embodimentsthereof with reference to the accompanying drawings, wherein:

FIG. 1 is a circuit diagram showing a configuration of a load drivingcircuit into which a booster device according to the present inventionis installed;

FIG. 2 is a circuit diagram showing a configuration of a booster deviceaccording to an embodiment of the present invention;

FIG. 3 is a characteristic view showing changes in voltages VB, VBB andbase voltages of transistors Q1, Q10 in the booster device according tothe embodiment of the present invention;

FIG. 4 is a characteristic view showing a part of a time zone of thecharacteristic view shown in FIG. 3 in an enlarged manner;

FIG. 5 is another characteristic view showing a part of a time zone ofthe characteristic view shown in FIG. 3 in an enlarged manner; and

FIG. 6 is a circuit diagram showing a configuration of a load drivingcircuit in the related art.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

An embodiment of the present invention will be explained with referenceto the drawings hereinafter. FIG. 1 is a circuit diagram showing aconfiguration of a load driving circuit into which a booster deviceaccording to the present invention is installed. As shown in FIG. 1, inthis load driving circuit, an N-type MOSFET (T1) is provided between abattery 16 (DC power supply) of the output voltage VB and the load Rz,and the drive/stop of the load Rz is controlled by switching ON/OFF ofthe MOSFET (T1). A gate of the MOSFET (T1) is connected to a control IC11 (electronic control circuit).

Also, a point P1 as a connection point between a positive-side terminalof the battery 16 and a drain of the MOSFET (T1) is connected to GND viathe diode DA1, the resistor RA1, and the capacitor CA1. Also, a point P2(the voltage VBB) as a connection point between the resistor RA1 and thecapacitor CA1 is connected to the control IC 11. A booster device 17 isprovided between the point P1 and the point P2.

Also, the control IC 11 includes a charge pump 12 for driving the N-typeMOSFET (T1), an overcurrent protection circuit 13 for protecting theMOSFET (T1) and wirings of the load circuit from the overcurrent, acontrol logic circuit 14, and a driver 15 for outputting a drivingsignal to a gate of the MOSFET (T1). Also, ON/OFF of the MOSFET (T1) canbe switched by the ON/OFF operation of the switch SW1.

FIG. 2 is a circuit diagram showing a detail configuration of thebooster device 17 as a feature portion of the present invention. Asshown in FIG. 2, the booster device 17 includes a clamp circuit 21, anoscillation circuit 22, and a booster circuit 23.

The clamp circuit 21 is arranged between the point P2 (the voltage VBB)and GND, and has a series connection of a resistor R21 and a resistorR22, and a Zener diode ZD1. Also, the clamp circuit 21 has a transistorQ10 (first switching element). A base of the transistor Q10 is connectedto a connection point between the resistor R21 (first resistor) and theresistor R22 (second resistor).

Also, in the clamp circuit 21, a Zener voltage of the Zener diode ZD1and resistance values of the resistors R21, R22 are set appropriately.Thus, when a voltage at the point P2 is higher than a predeterminedvoltage, a voltage across the resistor R22 can be set to exceed 0.6 V bysetting the Zener voltage and the resistance values. In the presentembodiment, this predetermined voltage is set to a threshold voltage Vth(e.g., 7.2 V) that is higher than the lowest operating voltage of thecontrol IC 11. That is, the Zener voltage of the Zener diode ZD1 and theresistance values of the resistors R21, R22 are set such that thetransistor Q10 is turned ON (a drive disabling signal is output) whenthe voltage VBB at the point P2 is more than the threshold voltage Vthwhereas the transistor Q10 is turned OFF (a drive enabling signal isoutput) when the voltage VBB is below the threshold voltage Vth.

Here, in FIG. 2, a numerical value set forth under each reference symboldenotes a concrete value of each element. For example, “20K” set forthunder the resistor R21 denotes that the resistance of 20 KΩ is used asan example of this resistor R21.

The oscillation circuit 22 is provided between the point P2 and GND. Theoscillation circuit 22 has a series-connected circuit having a resistorR1 (third resistor), a resistor R2 (fourth resistor), and a transistorQ1 (second switching element), and a series-connected circuit having aresistor R5 (fifth resistor), a resistor R6 (sixth resistor), and atransistor Q2 (third switching element). Both emitters of thetransistors Q1 and Q2 are connected mutually at a point P3. Also, thispoint P3 is connected to GND via a resistor R3 (seventh resistor). Also,a collector of the transistor Q1 is connected to a base of thetransistor Q2 via a resistor R4 (twelfth resistor). In this case, aresistance value of the resistor R6 is set smaller than a resistancevalue of the resistor R2. That is, R2 (120 KΩ)>R6 (20 KΩ).

A base of the transistor Q1 is connected to a collector of the foregoingtransistor Q10, and also is connected to GND via a capacitor C1 (firstcapacitor).

Also, the oscillation circuit 22 has a series-connected circuit having atransistor Q3 (fourth switching element), a resistor R9 (eighthresistor), and a resistor R10 (ninth resistor). An emitter of thetransistor Q3 is connected to the point P2, and the resistor R10 isconnected to GND. A base of the transistor Q3 is connected to aconnection point of the resistor R1 and the resistor R2.

Also, a connection point of the resistor R9 and the resistor R10 isconnected to a base of a transistor Q5 (sixth switching element). Anemitter of the transistor Q5 is connected to GND, and a collector of thetransistor Q5 (point P4) is connected to an upper terminal (point P5) ofthe capacitor C1 in FIG. 2 via a resistor R8 (eleventh resistor), and adiode D2 (second diode).

Also, the oscillation circuit 22 has a series-connected circuit having atransistor Q4 (fifth switching element), a resistor R7 (tenth resistor),and a diode D1 (first diode). The diode D1 is connected to the point P5,and a base of the transistor Q4 is connected to a connection point ofthe resistor R5 and the resistor R6.

Also, in the oscillation circuit 22, the charging of the capacitor C1 isstarted when the transistor Q10 is in its OFF (when the drive enablingsignal is output), then the transistor Q1 is turned ON after thecharging of the capacitor C1 is completed, and at the same time thetransistor Q4 is turned OFF and the transistor Q5 is turned ON, and thusthe discharging of the capacitor C1 is started. The oscillation circuit22 can generate pulse signals at the point P4 by repeating the aboveoperation. The details will be described later.

Then, the booster circuit 23 has a capacitor C2 (second capacitor) and acapacitor C3 (third capacitor). One end of the capacitor C2 is connectedto the point P1 as a positive terminal of the battery 16 via a diode D3,and also is connected to the point P2 via a diode D4 and a diode D5.Also, the other end of the capacitor C2 is connected to GND via atransistor Q6.

One end of the capacitor C3 is connected to the point P1 via the diodeD4 and the diode D3, and also is connected to the point P2 via the diodeD5. Also, the other end of the capacitor C3 is connected to a point P4in the oscillation circuit 22.

Also, the booster circuit 23 has a series-connected circuit having aresistor R15, a resistor R16, and a resistor R17. The resistor R15 isconnected to the point P2, and the resistor R17 is connected to GND. Aconnection point of the resistor R16 and the resistor R17 is connectedto a base of the transistor Q6. A connection point of the resistor R15and the resistor R16 is connected to the point P4 via a diode D7.

Also, a series-connected circuit having a resistor R11 and a resistorR12 is connected to the point P1, and also is connected to the point P4via a diode D6. A connection point of the resistor R11 and the resistorR12 is connected to a base of a transistor Q7. An emitter of thetransistor Q7 is connected to the point P1, and a collector thereof isconnected to a terminal of the capacitor C2 which is a lower sideterminal in FIG. 2. The transistor Q7 is provided to connect a terminalof the capacitor C2 (a lower side terminal of the capacitor C2 in FIG.2) to the battery 16 when the capacitor C2 is brought into thenon-grounded state.

Also, a series-connected circuit having a resistor R13 and a resistorR14 is connected to the point P1, and the resistor R14 is connected to alower terminal of the capacitor C2 in FIG. 2. A connection point of theresistor R13 and the resistor R14 is connected to a base of a transistorQ8. An emitter of the transistor Q8 is connected to the point P1, and acollector of the transistor Q8 is connected to a lower terminal of thecapacitor C3 in FIG. 2. The transistor Q8 is provided to connect aterminal (a lower terminal of the capacitor C3 in FIG. 2) to the battery16 when the capacitor C3 is brought into the non-grounded state.

Next, an operation of the booster device 17 constructed as aboveaccording to the present embodiment will be explained hereunder. Theoutput voltage VB of the battery 16 shown in FIG. 2 causes the capacitorCA1 to charge via the diode DA1 and the resistor RA1, and generates thestabilized voltage VBB at the point P2 (voltage supply point). Thisvoltage VBB is given by VBB=VB−Vf1, where the forward voltage of thediode DA1 is Vf1, and the voltage VBB becomes lower than the outputvoltage VB of the battery 16. In this case, a voltage drop in theresistor RA1 can be neglected because a resistance value of the resistorRA1 is very small (in the present embodiment, 3.9 Ω).

Then, the output voltage VB of the battery 16 is decreased, andaccordingly the voltage VBB is decreased. When the voltage VBB fallsbelow the threshold voltage Vth (VBB<Vth), the booster device 17 raisesthe voltage VBB at the point P2 by the operation described later. Thevoltage VBB is fed to the control IC 11 (see FIG. 1), and an electricpower is consumed by the control IC 11. A resistor R20 shown in FIG. 2indicates an equivalent resistor of the control IC 11, and a boostingcapability of the booster device 17 must be enhanced as the resistor R20becomes smaller.

Then, an operation of the clamp circuit 21 will be explained concretelyhereunder. In the clamp circuit 21 shown in FIG. 2, when the voltage VBBexceeds the Zener voltage of the Zener diode ZD1, an electric currentflows through the route of the voltage VBB→the Zener diode ZD1→theresistor R21→the resistor R22→GND. Then, when a voltage drop in theresistor R22 exceeds 0.6 V, the transistor Q10 is turned ON. Theresistance values of the resistors R21, R22 and the Zener voltage of theZener diode ZD1 are set in such a way that the voltage VBB at this timebecomes equal to the threshold voltage Vth.

In the period that the transistor Q10 is in its ON state, thenon-grounded terminal (in FIG. 2, the upper terminal) of the capacitorC1 provided to the oscillation circuit 22 is connected to GND via thetransistor Q10, and simultaneously a base of the transistor Q1 isgrounded. Therefore, an OFF state of the transistor Q1 is maintained,and thus the charging of the capacitor C1 is not started. As a result,an operation of the oscillation circuit 22 is stopped. That is, when thevoltage VBB is in excess of the threshold voltage Vth, the drivedisabling signal is output to the oscillation circuit 22.

Next, an operation of the oscillation circuit 22 will be explainedhereunder. As described above, when the voltage VBB at the point P2 isin excess of the threshold voltage Vth (VBB≧Vth), the transistor Q10 ofthe clamp circuit 21 is turned ON. Therefore, the transistor Q1 is heldin its OFF state, and the oscillation operation is stopped. At thistime, the transistor Q2 is held in its ON state, the transistor Q3 isheld in its OFF state, the transistor Q4 is held in its ON state, andthe transistor Q5 is held in its OFF state. As a result, the voltage atthe point P4 as a connection point of the transistor Q5 and the resistorR8 is kept at an L level, and thus the boosting operation is notexecuted by the booster circuit 23.

Also, when the voltage at the point P3 as the emitters of thetransistors Q1, Q2 is assumed as VAH and a base-emitter voltage of thetransistor Q4 is assumed as 0.6 V, the voltage VAH can be given by afollowing equation (1).VAH=(VBB−0.6)*R3/(R3+R6)  (1)

Here, when the voltage VBB at the point P2 is below the thresholdvoltage Vth (VBB<Vth), the transistor Q10 is turned OFF, and thus theclamp of the base voltage of the transistor Q1 is released. Accordingly,the grounded state of the point P5 as the non-grounded terminal of thecapacitor C1 is released. Then, as described above, since the transistorQ4 is still in its ON state, an electric current flows through the routeof the voltage VBB→the transistor Q4→the resistor R7→the diode D1→thecapacitor C1→GND, and thus the charging of the capacitor C1 is started.

When a voltage of the non-grounded terminal (point P5) of the capacitorC1 is assumed as VC1, this voltage VC1 is increased because the chargingof the capacitor C1 is started. When VC1=VAH+0.6 is attained, thetransistor Q1 is turned ON. Accordingly, the transistor Q2 is turnedOFF. Also, because the transistor Q1 is turned ON, the transistor Q3 andthe transistor Q5 are turned ON, and thus the voltage at the point P4 isat a low level.

When a voltage at the point P3 at this time is assumed as VAL and abase-emitter voltage of the transistor Q3 is assumed as 0.6 V, thevoltage VAL can be given by a following equation (2).VAL=(VBB−0.6)*R3/(R3+R2)  (2)

Here, since R6<R2 as described above, a relation between the equation(1) and the equation (2) is given by VAH>VAL.

Also, since the transistor Q2 is turned OFF, the transistor Q4 is turnedOFF. Also, since the transistor Q1 is turned ON, both the transistorsQ3, Q5 are turned ON. Accordingly, the charging route of the abovecapacitor C1 through the route of the voltage VBB→the transistor Q4→theresistor R7→the diode D1→the capacitor C1→GND is shut off, and thedischarging of the electric charges that are charged in the capacitor C1through the route of the capacitor C1→the diode D2→the resistor R8→thetransistor Q5→GND is started. As a result, a base voltage of thetransistor Q1 is decreased, and then the transistor Q1 is turned OFFwhen VC1−0.6=VAL is attained. Accordingly, the transistor Q5 is turnedOFF, and an electric potential of the point P4 is pulled up through theroute of the output voltage VB→the resistor R11→the resistor R12→thediode D6→the point P4, and thus the voltage at the point P4 goes to aHigh level.

Then, since the transistor Q3 is turned OFF and also the transistor Q5is turned OFF, the discharging route of the capacitor C1 is shut down.Also, since the transistor Q2 is turned ON and thus the transistor Q4 isturned ON, the above charging route of the capacitor C1 isreconstructed.

The capacitor C1 is charged, and then the electric charges are suppliedto the point P2 by the operation of the booster circuit 23 (the detailswill be described later) in the course of the subsequent discharge.Therefore, the voltage VBB is increased. Thus, the transistor Q10 in theclamp circuit 21 is turned ON, and the transistor Q1 is clamped once.However, the voltage VBB is decreased immediately, and thus thetransistor Q10 is turned OFF. Therefore, the clamp of the transistor Q1is released so that the charging operation of the capacitor C1 isrestarted and the transistor Q1 is turned on when VC1 becomes greaterthan the voltage specified by VAL+0.6V.

Also, when the voltage VBB is decreased due to a large power consumptionin the resistor R20 (corresponding to the control IC 11) so that VBB ismuch smaller than Vth, VBB<Vth is kept even though the boostingoperation is executed by ON/OFF of the transistor Q5. As a result, theoscillation circuit 22 performs the continuous operation without a haltperiod (i.e., the clamping operation of the clamp circuit 21 does notoccur).

When the above operation is repeated, the voltage at the point P4repeats alternately “High Level” and “Low Level”. Accordingly, the pulsesignal is output to the booster circuit 23.

In other words, in the oscillation circuit 22, when the clamping of theclamp circuit 21 is released once, the charging/discharging of thecapacitor C1 is repeated by the ON/OFF actions of the transistors Q1, Q2and the ON/OFF action of the transistor Q10. According to these actions,the “High Level” and “Low Level” are repeated alternately at the pointP4 to generate the pulse signal, and this pulse signal is output to thebooster circuit 23.

Next, an operation of the booster circuit 23 will be explainedhereunder. When the pulse signal being output from the oscillationcircuit 22 is at “High Level” (the transistor Q5 is in its OFF state),the transistor Q6 is turned ON by the voltage generated by the resistorR17, and a lower terminal of the capacitor C2 in FIG. 2 is grounded. Atthis time, since the transistor Q7 is still in its OFF state, someelectric charges are accumulated in the capacitor C2 by the voltage VBthat is fed from the battery 16.

Then, when the pulse signal is switched to “Low Level” (the transistorQ5 is turned ON), a connection point of the resistor R15 and theresistor R16 is connected to GND via the diode D7. Therefore, thetransistor Q6 is turned OFF and the capacitor C2 is brought into anon-grounded state, and also the transistor Q7 is turned ON. Also, alower terminal of the capacitor C3 in FIG. 2 is connected to GND via thetransistor Q5. Therefore, the electric charges accumulated in thecapacitor C2 are moved to the capacitor C3 via the diode D4. That is,the electric charges accumulated in the capacitor C2 are moved to thecapacitor C3, and are accumulated in the capacitor C3.

Then, when the pulse signal is switched to “High Level” again, a lowerterminal of the capacitor C2 in FIG. 2 is grounded, and a lower terminalof the capacitor C3 in FIG. 2 is disconnected from GND, and then thetransistor Q8 is turned ON. Therefore, the electric charges areaccumulated again in the capacitor C2 by the voltage supplied from thebattery 16, and also the electric charges accumulated in the capacitorC3 are supplied to the point P2 via the diode D5.

That is, when the pulse signal that is switched to “Low Level” and “HighLevel” alternately is supplied to the booster circuit 23 from theoscillation circuit 22, the electric charges are accumulated into thecapacitor C2 every one period of the pulse signal. The electric chargesare moved to the capacitor C3 and accumulated therein, and the electriccharges accumulated in the capacitor C3 are supplied to the point P2.Then, the voltage VBB at the point P2 is increased by the supply ofthese electric charges.

From the above, it is appreciated that, when the voltage VBB at thepoint P2 falls below the threshold voltage Vth, the clamping of theclamp circuit 21 is released and the pulse signal is output from theoscillation circuit 22 and then, when the pulse signal is supplied tothe booster circuit 23, the electric charges are supplied to the pointP2 and thus the voltage VBB at the point P2 is raised. In other words,when the voltage VBB at the point P2 is decreased, this voltage VBB canbe raised.

Then, when the voltage VBB is increased and reaches the thresholdvoltage Vth steadily, the transistor Q1 is clamped in its OFF state bythe clamp circuit 21. Therefore, the booster circuit 23 is not operatedand the further supply of electric charges is stopped.

Next, the simulation results obtained when the booster device 17 shownin FIG. 2 is operated will be explained with reference to FIGS. 3 to 5hereunder. FIG. 3 is a timing chart showing respective changes in thevoltage VB (curve S1), the voltage VBB at the point P2 (curve S2), thebase voltage of the transistor Q10 (curve S4), and the base voltage ofthe transistor Q1 (curve S3). FIG. 3 shows the case where the voltage VBis changed in the way of 10V→3.5V→10V. Also, the threshold voltage Vthto be set in the clamp circuit 21 is set to 7.2 V.

Also, FIG. 4 is an enlarged view showing a waveform in a time intervalfrom 15.0 ms to 20.0 ms in FIG. 3. Also, FIG. 5 is an enlarged viewshowing a waveform in a time interval from 30.0 ms to 40.0 ms in FIG. 3.

In FIG. 3, the simulation is started from a point of time t=0 ms atVB=10 V and VBB=9.2 V. The voltage VB starts to fall down from t=10 ms,and correspondingly the voltage VBB also starts to fall down. Because ofthe presence of the capacitor CA1 (33 μf), a voltage drop of the voltageVBB is delayed from the output voltage VB of the battery 16. When thevoltage VBB is decreased to 7.2 V (the threshold voltage Vth), the basevoltage of the transistor Q10 is decreased. Then, the oscillationcircuit 22 starts the operation.

As a result, even though the output voltage VB of the battery 16 isdecreased, the voltage VBB is held at a constant voltage (=7.2 V). Thebase voltage of the transistor Q10 is 680 mV at the voltage VBB=9.2 V,and is decreased to 650 mV at the voltage VBB=7.2 V at which theoscillation circuit 22 starts the operation. Then, the base voltage ofthe transistor Q10 is decreased to 610 mV while the output voltage VB ofthe battery 16 goes to VB=3.5 V, but the base voltage of the transistorQ10 never falls below this value, that is 610 mV, as far as the voltageVBB=7.2 V is kept.

In this case, the base voltage of the transistor Q10 shows a very smallchange of voltage, e.g., this voltage is decreased from 680 mV to 610mV. Hence, this base voltage shows a change that does not appearobviously in the scale (one division is 4V) in FIG. 3 to FIG. 5.Therefore, in FIG. 3 to FIG. 5, an interval in which the base voltage ofthe transistor Q10 is varying is indicated with a thick line. That is,in the interval indicated with a thick line, the base voltage of thetransistor Q10 shows a waveform that is varied vertically within a rangeof about several tens mV.

Also, as shown in FIG. 4, the oscillating action is started at t=17.5ms, and an oscillation period is shortened gradually as the outputvoltage VB of the battery 16 falls down. Then, as shown in FIG. 5, it isappreciated that, when the output voltage VB is increased from 3.5 V,the oscillation period is prolonged gradually. This is because a clamptime which is created in the clamp circuit 21 due to each pulse which isoutput from the oscillation circuit 22 is expanded longer as the outputvoltage VB becomes higher.

In this manner, in the booster device according to the presentembodiment, even in the situation that the output voltage VB of thebattery 16 is decreased and thus the voltage VBB at the point P2 isdecreased to the level at which the control IC 11 cannot be operatednormally, the booster circuit 23 operates to increase the voltage VBBwhen the voltage VBB falls below the threshold voltage Vth. Therefore,the control IC 11 can be operated normally.

Also, there is no necessity that the special IC that can operatenormally even when the voltage VBB is decreased should be employed.Therefore, it can be avoided that an increase in cost is brought aboutby such a situation.

With the above, the booster device of the present invention is explainedbased on the illustrated embodiment. But the present invention is notlimited to this embodiment, and configurations of respective portionscan be replaced by any configurations having the similar functionrespectively.

For example, in the above embodiment, an example that the battery thatis installed into the vehicle is employed as the DC power supply isexplained. But the present invention is not limited to this embodiment,and can be applied to the load circuit that employs other DC powersupply.

Industrial Applicability

The present invention is very useful in operating the IC normally byincreasing the voltage of the power supply when the voltage of the DCpower supply is decreased temporarily.

Although the invention has been illustrated and described for theparticular preferred embodiments, it is apparent to a person skilled inthe art that various changes and modifications can be made on the basisof the teachings of the invention. It is apparent that such changes andmodifications are within the spirit, scope, and intention of theinvention as defined by the appended claims.

The present application is based on Japanese Patent Application No.2009-099779 filed on Apr. 16, 2009, the contents of which areincorporated herein for reference.

1. A booster device for increasing a voltage at a voltage supply pointof a power supply circuit for supplying a driving voltage to anelectronic control circuit, the power supply circuit including a firstseries-connected circuit having a diode, a resistor, and a capacitorwhich is connected to a DC power supply, wherein one end of thecapacitor is connected to a ground and a connection point of theresistor and the capacitor serves as the voltage supply point, thebooster device comprising: a clamp circuit that outputs a drivedisabling signal when the voltage at the voltage supply point is equalto or greater than a predetermined threshold voltage, and outputs adrive enabling signal, which is generated by inverting the drivedisabling signal, when the voltage at the voltage supply point issmaller than the threshold voltage; an oscillation circuit that outputsa pulse signal when the drive enabling signal is output from the clampcircuit; and a booster circuit that increases the voltage at the voltagesupply point by supplying electric charges, which are accumulated by avoltage output from the DC power supply, to the voltage supply pointwhen the pulse signal is output from the oscillation circuit, whereinthe clamp circuit includes: a second series-connected circuit having aZener diode (ZD1), a first resistor (R21), and a second resistor (R22),and provided between the voltage supply point and the ground; and afirst switching element (Q10) having a control electrode which isconnected to a connection point of the first resistor and the secondresistor, and the first switching element is switched to ON/OFF inresponse to a voltage generated in the second resistor; and wherein theclamp circuit outputs the drive disabling signal when the firstswitching element is in an ON state, and outputs the drive enablingsignal when the first switching element is in an OFF state.
 2. A boosterdevice for increasing a voltage at a voltage supply point of a powersupply circuit for supplying a driving voltage to an electronic controlcircuit, the power supply circuit including a first series-connectedcircuit having a diode, a resistor, and a capacitor which is connectedto a DC power supply, wherein one end of the capacitor is connected to aground and a connection point of the resistor and the capacitor servesas the voltage supply point, the booster device comprising: a clampcircuit that outputs a drive disabling signal when the voltage at thevoltage supply point is equal to or greater than a predeterminedthreshold voltage, and outputs a drive enabling signal, which isgenerated by inverting the drive disabling signal, when the voltage atthe voltage supply point is smaller than the threshold voltage; anoscillation circuit that outputs a pulse signal when the drive enablingsignal is output from the clamp circuit; and a booster circuit thatincreases the voltage at the voltage supply point by supplying electriccharges, which are accumulated by a voltage output from the DC powersupply, to the voltage supply point when the pulse signal is output fromthe oscillation circuit, wherein the oscillation circuit includes: afirst capacitor which is charged when the drive enabling signal issupplied to the first capacitor; a second switching element which isturned ON based on a charging voltage of the first capacitor; and athird switching element which is turned OFF when the second switchingelement is turned ON; and wherein the first capacitor starts dischargingthereof when the third switching element is turned OFF, and startscharging thereof again when the second switching element is turned OFFdue to a voltage drop of the first capacitor and then the thirdswitching element is turned ON, so that repetition ofcharging/discharging operations outputs the pulse signal.
 3. A boosterdevice for increasing a voltage at a voltage supply point of a powersupply circuit for supplying a driving voltage to an electronic controlcircuit, the power supply circuit including a first series-connectedcircuit having a diode, a resistor, and a capacitor which is connectedto a DC power supply, wherein one end of the capacitor is connected to aground and a connection point of the resistor and the capacitor servesas the voltage supply point, the booster device comprising: a clampcircuit that outputs a drive disabling signal when the voltage at thevoltage supply point is equal to or greater than a predeterminedthreshold voltage, and outputs a drive enabling signal, which isgenerated by inverting the drive disabling signal, when the voltage atthe voltage supply point is smaller than the threshold voltage; anoscillation circuit that outputs a pulse signal when the drive enablingsignal is output from the clamp circuit; and a booster circuit thatincreases the voltage at the voltage supply point by supplying electriccharges, which are accumulated by a voltage output from the DC powersupply, to the voltage supply point when the pulse signal is output fromthe oscillation circuit, wherein the oscillation circuit includes thefirst capacitor provided between an output terminal of the clamp circuitand the ground, a parallel circuit, a third series-connected circuit, afourth series-connected circuit and a fifth series-connected circuit;wherein the parallel circuit includes a first series connection having athird resistor, a fourth resistor, and a second switching element and asecond series connection having a fifth resistor, a sixth resistor, anda third switching element; wherein the first series connection isconnected in parallel with the second series connection, one end of theparallel circuit is connected to the voltage supply point and other endof the parallel circuit is connected to a seventh resistor; wherein acontrol electrode of the second switching element is connected to anoutput terminal of the clamp circuit, and one end of the secondswitching element is connected to the control electrode of the thirdswitching element via a twelfth resistor; wherein the thirdseries-connected circuit includes a fourth switching element whosecontrol electrode is connected to a connection point of the thirdresistor and the fourth resistor, an eighth resistor, and a ninthresistor, one end of the third series-connected circuit is connected tothe voltage supply point and other end of the third series-connectedcircuit is connected to the ground; wherein the fourth series-connectedcircuit includes a fifth switching element whose control electrode isconnected to a connection point of the fifth resistor and the sixthresistor, a tenth resistor, and a first diode, and one end of the fourthseries-connected circuit is connected to the voltage supply point andother end of the fourth series-connected circuit is connected to theoutput terminal of the clamp circuit; wherein the fifth series-connectedcircuit includes a second diode, an eleventh resistor, and a sixthswitching element, and one end of the fifth series-connected circuit isconnected to the output terminal of the clamp circuit and other end isconnected to the ground; wherein a control electrode of the sixthswitching element is connected to a connection point of the eighthresistor and the ninth resistor; and wherein a connection point of theeleventh resistor and the sixth switching element serves as an outputpoint of the pulse signal.
 4. A booster device for increasing a voltageat a voltage supply point of a power supply circuit for supplying adriving voltage to an electronic control circuit, the power supplycircuit including a first series-connected circuit having a diode, aresistor, and a capacitor which is connected to a DC power supply,wherein one end of the capacitor is connected to a ground and aconnection point of the resistor and the capacitor serves as the voltagesupply point, the booster device comprising: a clamp circuit thatoutputs a drive disabling signal when the voltage at the voltage supplypoint is equal to or greater than a predetermined threshold voltage, andoutputs a drive enabling signal, which is generated by inverting thedrive disabling signal, when the voltage at the voltage supply point issmaller than the threshold voltage; an oscillation circuit that outputsa pulse signal when the drive enabling signal is output from the clampcircuit; and a booster circuit that increases the voltage at the voltagesupply point by supplying electric charges, which are accumulated by avoltage output from the DC power supply, to the voltage supply pointwhen the pulse signal is output from the oscillation circuit, whereinthe booster circuit includes a second capacitor (C2) and a thirdcapacitor (C3), one ends of which are connected to the DC power supplyand other ends of which repeat alternately grounded/non-grounded statesin accordance with a change of ON/OFF of the pulse signal; wherein thebooster circuit supplies electric charges, which are charged when theother end of the second capacitor (C2) is grounded, to the thirdcapacitor (C3) when the other end of the second capacitor (C2) ischanged into the non-grounded state, and charges the electric charges,which are supplied from the second capacitor (C2) into the thirdcapacitor (C3) when the other end of the third capacitor (C3) isgrounded; and wherein the booster circuit supplies the electric chargesto the voltage supply point (P2) to increase the voltage at the voltagesupply point (P2) when the other end of the third capacitor (C3) ischanged into the non-grounded state.